Arm & Hammer baking soda has an indefinite shelf life when stored properly, meaning it can last for many years if kept in a cool, dry place and sealed tightly. However, for optimal effectiveness, it is generally recommended to use baking soda within three years of purchase. Over time, baking soda can lose its potency, particularly if exposed to moisture, heat, or strong odors. To test if the baking soda is still good, one can mix a small amount with vinegar or lemon juice. If it bubbles vigorously, it is still active and can be used for baking or household cleaning. If there is little or no reaction, it may be time to replace it. Arm & Hammer provides clear packaging dates to help consumers gauge freshness, so it may be useful to check those as well. For more detailed information, one could explore the current web page where helpful resources and tips may be available.